Previous studies have demonstrated the proliferation of cells, presumably derived from the intramural pericytes, when isolated retinal microvessels are placed in culture medium. Recently, we have found that well differentiated endothelial cells also proliferate in these cultures under certain conditions. This proposal describes experiments in which we will attempt to extend our work on the growth properties, anatomy, and biochemistry of these cultured cells and of freshly isolated microvessel fragments. We will continue to investigate factors that may stimulate proliferation of microvessel cells. Of particular interest will be the effects of fibroblast growth factor. Anatomic studies will employ transmission electron microscopy to compare characteristics of cultured pericytes and endothelial cells in response to various hormones as well as to elevated levels of glucose and other sugars. In particular we will study alterations of the junctional complexes in cultured endothelial cells. We now have evidence that bovine pericytes in culture produce collagen and probably also basement membrane material. We expect that further experiments will demonstrate the same to be true of cultured capillary in our culture system. Anatomic investigations of isolated microvessel fragments from animals and from human autopsy specimens will evaluate, in particular, basement membrane morphology using scanning electron microscopy with correlative transmission electron microscopy of normal and diabetic human retinal and cerebral microvessel specimens. Finally, we will compare the respones of cultured pericytes and endothelial cells to various lectins, including particularly wheat germ agglutinin. In the presence of this lectin, cultured pericytes form large vacuoles, similar to those that have been described in cultured macrophages exposed to concanavalin A. We will compare the effects of these two lectins on pinocytic and phagocytic properties of cultured retinal pericytes and endothelial cells, with the goal of understanding the role of cell surface glycoproteins in mediating these functions.